Given a day of the month, return a stringified representation of it

addNumberSuffix.js

Array.prototype.contains = function(elem)
{
	return (this.indexOf(elem) === -1) ? false : true;
}
function addNumberSuffix(n)
{
	var suffix = '';
	n = parseInt(n);
	var number_last_digit = parseInt((''+n).substr(-1,1));
	if( [4,5,6,7,8,9,0].contains(number_last_digit) || (n > 10 && n < 14) )
	{
		suffix = 'th';
	}
	else if( number_last_digit === 1 )
	{
		suffix = 'st';
	}
	else if( number_last_digit === 2 )
	{
		suffix = 'nd';
	}
	else if( number_last_digit === 3 )
	{
		suffix = 'rd';
	}
	return '' + n + suffix;
}